Download lecture - McLoon Lab - University of Minnesota

Neuroscience 101
Steven McLoon
Department of Neuroscience
University of Minnesota
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Coffee Hour
Monday, Sept 12, 8:30-9:30am
at Caribou Coffee
917 Washington Ave. SE
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Major Cell Types of the Nervous System
 Neurons
 Macroglia
o Oligodendrocytes & Astrocytes (CNS)
o Schwann Cells & Satellite Cells (PNS)
 Microglia
 Cells associated with blood & vessels
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Anatomy of a ‘Typical’ Neuron
 Soma (cell body)
 Dendrites
 Axon (only one, but can branch)
 Synapses
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Anatomy of a ‘Typical’ Neuron
 Neurons come in many shapes and sizes
(i.e. there is no ‘typical neuron’).
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Anatomy of a ‘Typical’ Neuron
 Neurons have large amounts of rough
endoplasmic reticulum (rER) or Nissl
substance in their somas and larger dendrites.
 Many neurotransmitters as well as various
vesicle and structural proteins are synthesized
in the soma and delivered to the axon and
synaptic terminals via axoplasmic transport.
 Axoplasmic
transport goes
anterograde and
retrograde.
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Neurons communicate with other cells via synapses.
• Flow of information:
dendrite > soma > axon > synapse
• Neurotransmitter is released from the presynaptic cell at the synapse.
• The transmitter diffuses across the synaptic cleft to the postsynaptic cell.
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Neurons communicate with other cells via synapses.
Neurons communicate via synapses with:
 Neurons
o Axodendritic synapses
o Axonsomatic synapses
o Axonaxonic synapses
o Dendrodendritic synapses
 Other cell types (e.g. muscle, gland, blood vessel)
o Neuromuscular synapses
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Neurons communicate with other cells via synapses.
Structure of a typical synapse:
 Presynaptic terminal
o Synaptic vesicles containing
neurotransmitter
o Presynaptic density
 Synaptic cleft
 Postsynaptic element
o Neurotransmitter receptors
o Postsynaptic density
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Neurons communicate with other cells via synapses.
 An individual neuron can have one to thousands
of synapses.
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Neurons communicate with other cells via synapses.
 Many neurons have dendritic spines for receiving
synapses.
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Neurons communicate with other cells via synapses.
 Different types of neurons release different
neurotransmitters.
 Some common neurotransmitters:
class
transmitter
biogenic amines acetylcholine
dopamine
norepinephrine (noradrenaline)
epinephrine (adrenaline)
serotonin
amino acids
γ-aminobutyric acid (GABA)
glutamate
glycine
peptides
vasoactive intestinal polypeptide
substance P
enkephalin
endorphin
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Neurons communicate with other cells via synapses.
 Neurochemical communication
requires the postsynaptic terminal to
have the proper receptor for the
neurotransmitter.
 The transmitter-receptor pair
determines whether the active
synapse will excite (depolarize) or
inhibit (hyperpolarize) the
postsynaptic cell.
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Electrical Properties of Neurons
 A neuron at rest, that is a neuron receiving no
synaptic
input,
maintains
a
higher
concentration of K+ and a lower concentration
of Na+ and Cl- in its cytoplasm than outside the
cell.
 A sodium-potassium pump maintains this ion
differential.
 A ‘resting membrane potential’ can be
measured with electrodes on the inside and
outside of the cell; this is typically -65mV.
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Electrical Properties of Neurons
 Activation of neurotransmitter receptors causes
changes in the ion conductance in the
dendrites and soma.
 Inhibitory synaptic activity hyperpolarizes the
neuron (i.e. the membrane potential becomes
more negative).
 Excitatory synaptic activity depolarizes the
neuron (i.e. makes it more positive).
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Electrical Properties of Neurons
 The graded effect of all the synapses is
summed at the initial segment of the axon.
 When the initial segment becomes sufficiently
depolarized, voltage-gated sodium channels
open and an action potential is generated.
 The influx of Na+ into the axon is followed by
an outflow of K+.
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Electrical Properties of Neurons
 The influx of Na+ into one
segment of the axon results
in opening of the sodium
channels in the next part of
the axon.
 The action potential is self
propagated down the axon.
 When an action potential
reaches the synapse, it
initiates
release
of
neurotransmitter into the
synaptic cleft.
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Astrocytes
 Star-shaped glial cells in the CNS
 Most abundant cell type of the brain and
spinal cord
 Surround most synaspes
Functions of astrocytes:
 Contribute to the cellular scaffolding
 Secrete extracellular matrix molecules
 Provide trophic support for neurons
 Form external limiting membrane of brain
& spinal cord
 During development, serve as progenitor
cells & guide cell migration
 Following injury or disease, phagocytize
cellular debris & form glial scar
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Astrocytes
 Mediate exchange between
capillaries and neurons;
contribute to the blood-brain
barrier
 Regulate local blood flow
 Contribute to neuronal
metabolism via lactate shuttle &
storing glucose as glycogen
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Astrocytes
 Regulate the extracellular ionic
environment, which modulates synaptic
transmission & plasticity
 Remove & recycle neurotransmitter
 ‘Insulate’ synapses (i.e. prevent
transmitter spillover)
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Myelin
Myelin or a wrapping of glial cell
membranes around axons is
formed by:
 Schwann cells in the PNS
 Oligodendrocytes in the CNS
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Myelin
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Myelin
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Myelin
 Myelin allows saltatory conduction
or rapid advance of the action
potential down the axon.
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Development of Myelin
 Glial cells wrap around the axons, synthesize the
molecules associated with myelin-type membrane,
and exclude cytoplasm from all but the mesaxon and
soma
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Development of Myelin
• Some tracts myelinate as early as
14wks
of
gestation;
myelination
continues until mid-adolescence.
• Babinski sign is present in newborns
and disappears as pyramidal tract
myelinates (4mos – 2yrs of age); also
associated with upper motor neuron
disease in adults.
• Many factors can delay myelination
including poor nutrition.
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Nervous System Organization
 Peripheral nervous system (PNS) includes
nerves and ganglia.
o Nerves are bundles of axons.
o Nerves connect to the brain (cranial nerves)
or to the spinal cord (spinal nerves).
o Ganglia are collections of neuronal cell
bodies.
 Central nervous system (CNS) includes the
brain, spinal cord and retina.
o Tracts are bundles of axons (white matter).
o Neuronal cell bodies are in nuclei or layered
structures (grey matter).
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Nervous System Organization
 Central nervous system (CNS) includes the
brain, spinal cord and retina.
o Tracts are bundles of axons (white matter).
o Neuronal cell bodies are in nuclei or layered
structures (grey matter).
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Major Brain Regions
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Systems
 Motor vrs sensory systems
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Systems
 Sensory systems
 Motor systems
o Somatosensory
o Somatic motor
o Visceral sensory
o Special motor
o Special sensory
o Autonomic (visceral)
 Vision
 Sympathetic
 Auditory
 Parasympathetic
 Vestibular
 Gustatory (taste)
 Olfactory (smell)
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Spinal Cord
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Spinal Cord
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Spinal Cord
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Motor Neuron
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Motor Neuron
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Somatosensory Neuron
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Somatosensory Neuron
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Autonomic System (motor)
 Two neuron chain:
o Preganglionic neuron in brainstem or
spinal cord
o Ganglion neuron in PNS ganglion
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Autonomic System (motor)
 Parasympathetics
o Cranial (brainstem) and sacral spinal
cord preganglionic neuron
o Axons exit via cranial nerves or ventral
roots
o Ganglion near target
 Sympathetics
o Thoracic and lumbar spinal cord
preganglionic neuron
o Axons exit spinal cord via ventral roots
o Ganglion along vertebral column
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Spinal Cord
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Spinal Cord
sympathetic ganglion
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What is PNS and what is CNS?
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Somatic & Special Motor Systems
 Upper motor neuron in motor cortex
(most axons cross to the opposite side of the body)
-synapses with (Lower) motor neuron in a cranial nerve nucleus in
the brainstem or the ventral horn of the spinal cord
(axons exit CNS via a cranial nerves or ventral
roots)
-synapses with Muscle fiber
(each muscle fiber has a single neuromuscular
synapse; a single motor neuron can innervate
multiple muscle fibers)
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Somatic & Special Motor Systems
 Motor neuron activity is influenced by many pathways
including sensory reflex arcs and diverse brain
structures (e.g. basal ganglia, pons, cerebellum).
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Sensory Systems General Plan
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Somatosensory System
 Small primary afferent axons for pain,
temperature, pressure and touch
(spinothalamic pathway)
dorsal root ganglion neuron
(axon enters spinal cord)
neuron in dorsal horn
(axon crosses and ascends to thalamus)
neuron in ventral posterior lateral nucleus
(axon ascends to cortex)
neuron in S1 (primary somatosensory)
layer IV
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Somatosensory System
 Large primary afferent axons for
proprioception, movement, discriminative
touch (dorsal column pathway)
dorsal root ganglion neuron
(axon ascends in spinal cord to medulla)
neuron in gracile or cuneate nucleus
(axon crosses and ascends to thalamus)
neuron in ventral posterior lateral nucleus
(axon ascends to cortex)
neuron in S1 (primary somatosensory)
layer IV
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Visual System
 Parts of the eye
Visual System
Retina:
- pigment epithelium
- neural retina
photoreceptor cells (rods &
cones)
synaptic layer
inner nuclear cells
(horizontal, bipolar &
amacrine)
synaptic layer
ganglion cells
optic fiber (axon) layer
- light path
- detached retina
Visual System
 Optic nerve (CN II)
blind spot / optic nerve head =
5-8° of arc of the visual field
Visual System
Optic nerve (CN II):
- function: special sensory – vision
retinal ganglion cell (in retina)
optic fiber layer (in retina)
optic nerve
[optic foramen]
optic chiasm (in brain)
optic tract (in brain)
< visual nuclei (in brain)
suprachiasmatic nucleus
(in hypothalamus for circadian
rhythm)
lateral geniculate nucleus
(in thalamus for vision)
pretectal nucleus
(at junction of thalamus & midbrain
for pupillary constriction & lens)
superior colliculus
(in midbrain for oculomotor & head
control)
Visual System
Visual System
Vision from each side of the visual field is carried to the opposite side of the brain.